Apparatus and method for visualizing digital breast tomosynthesis  and other volumetric images

ABSTRACT

Digital Breast Tomosynthesis allows for the acquisition of volumetric mammography images. The present invention allows for novel ways of viewing such images to detect microcalcifications and obstructions. In an embodiment a method for displaying volumetric images comprises computing a projection image using a viewing direction, displaying the projection image and then varying the projection image by varying the viewing direction. The viewing direction can be varied based on a periodic continuous mathematical function. A graphics processing unit can be used to compute the projection image and bricking can be used to accelerate the computation of the projection images.

PRIORITY CLAIM

This application claims priority to U.S. Provisional application No.62/197,956 filed Jul. 28, 2015, the specification and drawings of whichare herein expressly incorporated by reference in its entirety.

FIELD OF INVENTION

The invention pertains to novel ways of viewing volumetric images usedfor medical diagnosis.

BACKGROUND

Volumetric images play an increasingly important role in medicaldiagnosis including cancer treatments such as site directed chemotherapyand radiology. Volumetric images are being generated by a multitude ofdifferent devices, including Magnetic Resonance Imaging (MRI) scanners,see for example Nuclear magnetic resonance imaging apparatus, U.S. Pat.No. 4,534,358, or Computed Tomography (CT) scanners, see for examplePatients' support installation for a tomographic X-ray apparatus, U.S.Pat. No. 3,974,388, or certain C-Arm devices, see for example C-Armcomputerized tomography system, U.S. Patent Application Publication No.2010/0284601.

A certain class of these modalities, such as the CT scanner computes thevolumetric images from a series of 2D projections from different angles,see for example (i) Methods and Apparatus for Reconstruction of 3D ImageVolumes From Projection Images, U.S. Pat. No. 7,876,944; (ii) Method ofReconstructing Computer Tomography (CT) Volumes Suitable for Executionon Commodity Central Processing Units (CPUS) and Graphics Processors,and Apparatus Operating in Accordance with those Methods, U.S. Pat. No.7,778,392 and (iii) Method of Reconstructing Computer Tomography (CT)Volumes Suitable for Execution on Commodity Central Processing Units(CPUS) and Graphics Processors, and Apparatus Operating in Accordancewith those Methods, U.S. Pat. No. 8,107,592, which references (i)-(iii)are herein expressly incorporated by reference in their entireties.

A recent advance in the field is the development of a Digital BreastTomosynthesis (DBT) scanner which generates volumetric mammographyimages, see for example Integrated multi-mode mammography/tomosynthesisx-ray system and method, U.S. Pat. No. 7,869,563, which is hereinexpressly incorporated by reference in its entirety. Similar to CT orC-Arm devices, the DBT devices acquire a number of 2D X-Ray images, or2D projections, from different angles. From these projections avolumetric image is computed.

SUMMARY OF THE INVENTION

In an embodiment of the present invention, a method for displayingvolumetric images comprises computing a projection image using a viewingdirection, displaying the projection image and then varying theprojection image by varying the viewing direction. In an embodiment ofthe present invention, the viewing direction can be varied based on aperiodic continuous mathematical function. In an embodiment of thepresent invention, a graphics processing unit (GPU) can be used tocompute the projection image and bricking can be used to accelerate thecomputation of the projection images. In another embodiment of thepresent invention, a sequence of projections covering one period can berendered, cached and then played back one or more times, where therendering is carried out on a server and the caching and play back iscarried out on a client computer. A render server program is describedin U.S. application Ser. No. 13/831,967, entitled “Multi-User Mult-GPURender Server Apparatus and Methods”, which was filed Mar. 15, 2013 isherein expressly incorporated by reference in its entirety. A rule basedrender server program is described in “Method and System for Rule-BasedDisplay of Sets of Images” which issued as U.S. Pat. No. 8,976,190 onMar. 10, 2015, and is herein expressly incorporated by reference in itsentirety. In an alternative embodiment of the present invention, theviewing direction can be varied based on user input. In a differentembodiment of the present invention, a system that displays two or morevolumetric images by computing a projection image of each of thevolumetric images, using the same viewing direction v for eachvolumetric image, displaying each projection images, and varying theprojection image by varying the viewing direction, where the variedviewing direction is changed in the same way for each of theprojections. In an embodiment of the present invention, the volumetricimages are computed from a number of 2D X-Ray images, or 2D projections,from different angles generated by a DBT device. In an embodiment of thepresent invention, volumetric mammography images are displayed. In analternative embodiment of the present invention, volumetric images arecomputed from a number of 2D X-Ray images generated by angiography. Inan embodiment of the present invention, the volumetric cerebralangiography images of the human brain are displayed. In anotheralternative embodiment of the present invention, volumetric images arecomputed from a confocal microscope using antibody staining. In anembodiment of the present invention, volumetric cell tissue generated bythe confocal microscope is displayed.

BRIEF DESCRIPTION OF THE DRAWINGS

This invention is described with respect to specific embodimentsthereof. Additional features can be appreciated from the Figures inwhich:

FIG. 1A shows the specimen imaged using an X-Ray source from twopositions spanning an angular range;

FIG. 1B shows the specimen imaged using an X-Ray source and an X-Raydetector from a multitude of positions. The positions span a certainangular range that is defined by the physical constraints of the machineand the patient's position;

FIG. 2 illustrates the calculation of a projection P from the volumetricimage I, where the projection is defined by the viewing direction v,which defines the Projection plane, according to an embodiment of theinvention;

FIG. 3A shows a specimen with two areas of increased density, accordingto an embodiment of the invention;

FIG. 3B shows the two areas in FIG. 3A projected to the same spot in theprojection Image, according to an embodiment of the invention;

FIG. 3C shows the two areas in FIG. 3A projected to different spots inthe projection Image, according to an embodiment of the invention;

FIG. 4 shows how only a subset of the acquisition volume is covered bythe specimen, while other areas (hatched) only contain backgroundpixels, according to an embodiment of the invention;

FIG. 5 shows the volume subdivided into sub-volumes, according to anembodiment of the invention;

FIG. 6 illustrates the dynamic variation of the viewing direction vaccording to Equation 2, according to an embodiment of the invention;

FIG. 7A shows an artists impression of an image of a human breastcomputed from a number of images recreated from a specific angle where amicro calcification is occluded by denser breast tissue, according to anembodiment of the invention;

FIG. 7B shows an artists impression of an image of a human breast takenfrom a different angle to that shown in FIG. 7A, where the microcalcification is visible and not occluded by the denser breast tissue,according to an embodiment of the invention;

FIG. 8A shows an artists impression of a screen dump of a video image atapproximately the two (2) second time point, where the video shows adynamic comparison of a human breast computed from a number of imagesrecreated as the viewing direction is changed, where micro calcificationoccluded by denser breast tissue can be revealed, according to anembodiment of the invention;

FIG. 8B shows an artists impression of a screen dump of a video image atapproximately the five (5) second time point, where the video shows adynamic comparison of a human breast computed from a number of imagesrecreated as the viewing direction is changed, where micro calcificationoccluded by denser breast tissue can be revealed, according to anembodiment of the invention;

FIG. 8C shows an artists impression of a screen dump of a video image atapproximately the nine (9) second time point, where the video shows adynamic comparison of a human breast computed from a number of imagesrecreated as the viewing direction is changed, where micro calcificationoccluded by denser breast tissue can be revealed, according to anembodiment of the invention;

FIG. 8D shows an artists impression of a screen dump of a video image atapproximately the twelve (12) second time point, where the video shows adynamic comparison of a human breast computed from a number of imagesrecreated as the viewing direction is changed, where micro calcificationoccluded by denser breast tissue can be revealed, according to anembodiment of the invention;

FIG. 9A shows the artists impression of a screen dump of a video imageat at approximately the five (5) second time point shown in FIG. 8B,according to an embodiment of the invention;

FIG. 9B shows the artists impression of a screen dump of a video imageat approximately nine (9) second time point shown in FIG. 8C, accordingto an embodiment of the invention;

FIG. 10A shows the image of a human breast represented in FIG. 7A,according to an embodiment of the invention;

FIG. 10B shows the image of the human breast taken from a differentangle to that shown in FIG. 10A, represented in FIG. 7B, according to anembodiment of the invention;

FIG. 11A shows a screen dump from the mp3 video at approximately the two(2) second time point, represented in FIG. 8A, according to anembodiment of the invention;

FIG. 11B shows a screen dump from the mp3 video at approximately thefive (5) second time point, represented in FIG. 8B, according to anembodiment of the invention;

FIG. 11C shows a screen dump from the mp3 video at approximately thenine (9) second time point, represented in FIG. 8C, according to anembodiment of the invention;

FIG. 11D shows a screen dump from the mp3 video at approximately thetwelve (12) second time point, represented in FIG. 8D, according to anembodiment of the invention;

FIG. 12A shows the screen dump from the mp3 video at approximately thefive (5) second time point, as represented in FIG. 9A, according to anembodiment of the invention; and

FIG. 12B shows the screen dump from the mp3 video at approximately thenine (9) second time point, as represented in FIG. 9B, according to anembodiment of the invention.

DESCRIPTION OF THE INVENTION Definitions

The transitional term ‘comprising’ is synonymous with “including,”“containing,” or “characterized by,” is inclusive or open-ended and doesnot exclude additional, unrecited elements or method steps.

The transitional phrase ‘consisting of’ excludes any element, step, oringredient not specified in the claim, but does not exclude additionalcomponents or steps that are unrelated to the invention such asimpurities ordinarily associated with a composition.

The transitional phrase ‘consisting essentially of’ limits the scope ofa claim to the specified materials or steps and those that do notmaterially affect the basic and novel characteristic(s) of the claimedinvention.

The term ‘bandwidth’ and ‘send bandwidth’ refer to various bit-ratemeasures, representing the available or consumed data communicationresources expressed in bits per second or multiples of it.

The phrase ‘adaptive bandwidth management’ means methods thatcontinuously adjust the amount of data that is sent into a network pertime in order to avoid or reduce network congestion and transfer delay.

The term ‘client-server’ refers to a computer system that selectivelyshares its resources with ‘clients’. A ‘client’ is a computer orcomputer program that initiates contact with a ‘client-server’ or‘server’ in order to make use of the server resources. A client-servercan be especially useful to undertake volume rendering tasks. Such aserver can have one or more graphics processing units. Further, bysharing the server's computer resources, multiple clients can access anduse the server resources at the same time. Because a computer does alimited amount of work at any moment, a time-sharing system must quicklyprioritize its tasks to accommodate the clients. Clients and serversexchange messages in a request-response messaging pattern: The clientsends a request, and the server returns one or multiple responses,synchronously or asynchronously.

The term ‘video’ means the display of three (3) or more 2-D projectionimages where there is a time delay between the first 2-D projectionimage and a second 2-D projection image and a time delay between thesecond 2-D projection image and a third 2-D projection image. A videomay be displayed using a number of formats including avi, fly, H.262,H.263, H.264, m4v, mov, MPEG-1, MPEG-1 Part 2, MPEG-2, MPEG-4 Part 2,nsv, ogv, roq, vp6, vp8, vp9, webm, and wmv.

The phrase ‘host computer’ means a server or other processor withassociated memory. In an embodiment of the invention, a host computer isenabled to provide measured 2-D projection images to a client.

The term ‘caching’ means storing in memory. A generated projection imagefrom a volumetric image can be cached in one or both a client associatedmemory and a server associated memory, where the memory can be accessedrapidly by either the client processor or the server processorrespectively.

The phrase ‘measured 2-D projection image’ means a two-dimensional (2-D)scan of biological tissue produced by forward-projection orback-projection of medical imaging equipment as described in U.S. Pat.No. 8,107,592 to A. Berman, and U.S. Pat. No. 7,876,944 to D Stalling etal.

The phrase ‘volumetric image’ refers to a three-dimensional (3-D)representation reconstructed from the data produced from a series ofmeasured 2-D projection images or other 2-D representations of a tissue,an organ or an entity.

The term ‘reconstruction’ means generating a 3-D volumetric image basedon a plurality of measured 2-D projection images. The phrase‘reconstruction of a volumetric image’ means calculating a 3-Dvolumetric image based on a plurality of measured 2-D projection images.

The term ‘generated’ means constructing one or more generated 2-Dprojection images from a 3-D volumetric image. The phrase ‘generating animage’ or ‘generating a plurality of images’ means constructing one ormore generated 2-D projection images from a 3-D volumetric image. In anembodiment of the invention, the one or more generated 2-D projectionimages can be generated at different viewing directions.

The phrase ‘viewing direction’ means the line constructed passingthrough a viewing position to an object. As the designated positionchanges, the viewing direction changes. As shown in FIG. 1A a firstviewing direction 111 is generated by the line between position 110 andthe object 105. A second viewing direction 116 is generated by the linebetween position 115 and the object 105. The angle (θ) between the firstviewing direction 111 and the second viewing direction 112 increasesfrom 0 to θ. The smallest viewing direction is when the angle=0. Thelargest viewing direction is when the angle=θ.

The phrase ‘equivalent viewing direction’ means the same viewingdirection in the absence of physiologic changes in the tissue or anequivalent viewing direction when physiologic changes have occurred or acomparable tissue is utilized, where the equivalent viewing directioncan compensate for changes in the tissue in the body with time and/orcan compensate for the symmetry and asymmetry of different tissue in thebody. The equivalent viewing direction can be used to ascertain thepresence or absence of physiologic changes in the tissue with time, orwhen physiologic changes have occurred based on the inspection of acomparable tissue. The equivalent viewing direction can compensate forchanges in the tissue in the body with time and/or can compensate forthe symmetry and asymmetry of viewing projection images of differenttissues in the body.

The term ‘identifies’ refers to a 3D or 2D image corresponding to a viewthat is displayed and/or compared with other views that reveals or moreclearly elucidates a microcalcification or obstruction through one ormore processes selected from the group consisting of: observation by thehuman eye, identification by a segmentation algorithm, identification bya bricking algorithm. The phrase ‘improves the visual clarity ofidentification’ means a process or technique that compares or changesone or more projection images to allow an obstruction including a microcalcification to be identified in the one or more projection images.

Receiving a Volumetric Image

A computed tomography (CT) scan can generate many 2-D images taken fromdifferent angles around a scanned object to produce cross-sectional(tomographic) images (‘virtual slices’) of the scanned object.Alternatively, positron emission tomography (PET), single photonemission computed tomography (SPECT), computer assisted tomography (CAT)scanners or tomosynthesis systems can produce ‘measured projectionimages’. These measured 2-D projection images can be used to reconstructa ‘volumetric image’, where the virtual slices form a volumetric imageor 3-D image of the scanned object. The phrase ‘volumetric image’ refersto a 3-D representation reconstructed from the data produced byforward-projecting or back-projecting medical imaging equipment.Measured projection images can be measured by medical technologists, andcan be used to reconstruct a volumetric image and then the volumetricimage can be received by a physician in order to diagnose a patient.

In an embodiment of the invention, using the reconstructed 3-D image itis possible to form a generated 2-D projection image, that is, arepresentation can be generated from a volumetric image by identifying apoint source at a distinct focus and thereby a ‘projection direction’through the volume to a plane at which the respective generated 2-Dprojection image can be formed.

Computing a Plurality of Projection Images

One or more generated 2-D projection images can be generated from avolumetric image. Computing a plurality of generated 2-D projectionimages of the volumetric image using a plurality of viewing directionsbetween a first viewing direction and a second viewing direction can beused to produce generated 2-D projection images required by a physicianbut otherwise not revealed by a measured 2-D projection image.Alternatively, by generating a plurality of generated 2-D projectionimages, a dynamic view of the volumetric image can be generated, whichallows for better diagnosis than a single or static measured 2-Dprojection image or a single or static generated 2-D projection image.

Comparing a First Projection Image a Second Projection Image

The phrase ‘time comparison’ means comparing a projection image obtainedat a specific viewing direction with an earlier in time projection imageof a tissue obtained at an equivalent viewing direction of the sametissue. In an embodiment of the invention, a time comparison comparesone or more projection images of a right breast with one or moreprojection images of the same right breast measured at an earlier timepoint, where the projection images are generated at equivalent viewingdirections. In an embodiment of the invention, a time comparisoncompares one or more measured 2-D projection images of a right breastwith one or more generated 2-D projection images of the same rightbreast generated from a volumetric image reconstructed from a pluralityof measured 2-D projection images from an earlier time point, where theprojection images are generated at equivalent viewing directions. In analternative embodiment of the invention, a time comparison compares oneor more generated 2-D projection images of a right breast with one ormore measured 2-D projection images of the same right breast measured atan earlier time point, where the projection images are generated atequivalent viewing directions.

The phrase ‘structural comparison’ means comparing a projection imageobtained at a specific viewing direction with a projection image of atissue obtained at an equivalent viewing direction of a different butcomparable tissue. In an embodiment of the invention, a structuralcomparison compares one or more projection images of a right breast withone or more projection images of a left breast both viewed at equivalentviewing directions. In an embodiment of the invention, a structuralcomparison compares one or more generated 2-D projection images of aright breast with one or more generated 2-D projection images of a leftbreast, where each of the generated 2-D projection images are viewed atequivalent viewing directions. In an alternative embodiment of theinvention, a structural comparison compares one or more measured 2-Dprojection images of a right breast with one or more generated 2-Dprojection images of a left breast, where each of the measured andgenerated 2-D projection images are viewed at equivalent viewingdirections. In another embodiment of the invention, a structuralcomparison compares one or more generated 2-D projection images of aright breast with one or more measured 2-D projection images of a leftbreast, where each of the measured and generated 2-D projection imagesare viewed at equivalent viewing directions.

The phrase ‘dynamic comparison’ means comparing a series of projectionimages obtained at a variety of viewing directions. In an embodiment ofthe invention, a dynamic comparison compares one or more DBT projectionimages of a right breast that change in time as the viewing direction isscanned as a video. In an embodiment of the invention, the change inviewing direction can adjust for the type of tissue being scanned.

The phrase ‘visual comparison’ means time comparing, structurallycomparing, and/or dynamically comparing one or more projection imageswith the naked eye.

The phrase ‘direct comparison’ means one or more of time comparing,structurally comparing, and dynamically comparing one or more projectionimages using a computer to analyze changes in the intensity density of avoxel matrix represented by the projection images. In an embodiment ofthe invention, one or more generated 2-D projection images are comparedwith one or more measured 2-D projection images using one or more oftime comparing, structurally comparing, and dynamically comparing,wherein a computer is used to analyze changes in the intensity densityof a voxel matrix represented by the one or more generated 2-Dprojection images and the one or more measured 2-D projection images.

A first viewing direction 111 corresponds with the line between position110 and the object 105. A second viewing direction 116 corresponds withline between position 115 and the object 105 (see FIG. 1A). Theincrement 112 is the angle between the first viewing direction 111 andthe second viewing direction 112 (see FIG. 1A). By selecting a firstviewing direction, a first generated 2-D projection image can be formed.Similarly, selecting a second viewing direction allows a secondgenerated 2-D projection image at the second viewing direction to beformed. In an embodiment of the invention a first generated 2-Dprojection image can be dynamically compared with one or more secondgenerated 2-D projection images. In an alternative embodiment of theinvention a measured 2-D projection image can be dynamically comparedwith one or more generated 2-D projection images. In an alternativeembodiment of the invention, a first projection image can be timecompared with a second projection image measured at an earlier time. Inanother embodiment of the invention, a generated 2-D projection imagecan be time compared with a measured 2-D projection image measured at anearlier time. In another embodiment of the invention, a first projectionimage can be structurally compared with a second projection image of acontrol tissue. In another embodiment of the invention, a generated 2-Dprojection image can be structurally compared with a measured 2-Dprojection image of a control tissue. In an embodiment of the invention,a density map for the first projection image is visually compared with adensity map of the second projection image. In an embodiment of theinvention, a density map for a generated 2-D projection image isvisually compared with a density map of a measured 2-D projection image.In an alternative embodiment of the invention, a computer program isused to directly compare the density map for the first projection imagewith a density map of the second projection image. In anotheralternative embodiment of the invention, a computer program is used todirectly compare the density map for a generated 2-D projection imagewith a density map of a measured 2-D projection image.

Volume Rendering

Volume rendering, or reconstructing a volume, includes a variety ofstandard visualization methods including volume rendering techniques(VRT), shaded volume rendering techniques (sVRT), maximum intensityprojection (MIP), oblique slicing or multiplanar reformats (MPR),axial/sagittal and coronal slice display, and thick slices (also calledslabs). Within the scope of the invention, other methods and apparatusof forward-projection and back-projection can be used for generating aseries of measured 2-D projection images with which to reconstruct 3-Dvolumetric image representations, as described in U.S. Pat. No.9,019,287, which is herein expressly incorporated by reference in itsentirety.

In an embodiment of the invention, a computer chip, chip set, computerboard and/or computer processor can be configured as a ‘graphicsprocessing unit’ (GPU) to perform volume rendering and or to generateone or more reconstructed 2-D projection views from a volumetric image.In an embodiment of the invention, volume rendering includesinitializing to arbitrary values the volume density distribution in avoxel matrix, iteratively estimating and comparing with a measuredprojection, and then correcting each pixel based on the comparison asdescribed in U.S. Pat. No. 7,876,944.

Intensity Values

Image segmentation is an automated technique that facilitatesdistinguishing objects and other features in digital images. Thetechnique can be used, for example, to simplify digitized images so thatthey can be more readily interpreted by computers (e.g., image analysissoftware) and/or by their users. An image can be made up of pixelscontaining a wide range of undifferentiated intensity values thatalthough, possibly recognizable to the human eye as skeletal bones anddigestive tract are largely uninterpretable by a computer. In anembodiment of the invention, a comparison between a first projectionimage with a second projection image that reveals an area of increasedintensity values in the second projection image can indicate that thesecond viewing direction which generated the second projection imagereveals an unobstructed projection image. In an alternative embodimentof the invention, a comparison between a generated 2-D projection imagewith a measured 2-D projection image that reveals an area of increaseddifferentiated intensity values in the measured 2-D projection image canindicate that the viewing direction which formed the generated 2-Dprojection image reveals an unobstructed viewing direction. In analternative embodiment of the invention, a comparison between a firstprojection image with a second projection image that reveals an area ofincreased differentiated intensity values in the second projection imagecan indicate that the second viewing direction which generated thesecond projection image reveals an increased clarity projection image,as described in U.S. Pat. No. 8,548,215, which is herein expresslyincorporated by reference in its entirety. In an alternative embodimentof the invention, a comparison between a generated 2-D projection imagewith a measured 2-D projection image that reveals an area of increaseddifferentiated intensity values in the measured 2-D projection image canindicate that the viewing direction which formed the generated 2-Dprojection image reveals an advantageous viewing direction.

Primary Study Versus Secondary Study

A primary study is a study carried out at a specified time point. Asecondary study is a study carried out at a subsequent time point. In anembodiment of the invention, a computer chip, chip set, computer boardand/or computer processor can be configured as a ‘digita data processor’to perform volume rendering, to generate one or more projection viewsfrom a volume and or to compare two or more projection views. Thedigital data is generated by forward-projecting or back-projectingmedical imaging equipment used to generate measured projection images orother 2-D representations. In an embodiment of the invention, acomparison between a generated 2-D projection image from a secondarystudy with a generated 2-D projection image from a primary study thatreveals an area of increased differentiated intensity values can be usedto assess the development or changes occuring over time. In anembodiment of the invention, a comparison between a generated 2-Dprojection image from a secondary study with a measured 2-D projectionimage from a primary study that reveals an area of increaseddifferentiated intensity values in the measured 2-D projection image canindicate that the viewing direction which formed the generated 2-Dprojection image reveals an unobstructed viewing direction.

In the following description, various aspects of the present inventionwill be described. However, it will be apparent to those skilled in theart that the present invention may be practiced with only some or allaspects of the present invention. For purposes of explanation, specificnumbers, materials, and configurations are set forth in order to providea thorough understanding of the present invention. However, it will beapparent to one skilled in the art that the present invention may bepracticed without the specific details. In other instances, well-knownfeatures are omitted or simplified in order not to obscure the presentinvention.

Parts of the description will be presented in data processing terms,such as data, selection, retrieval, generation, and so forth, consistentwith the manner commonly employed by those skilled in the art to conveythe substance of their work to others skilled in the art. As is wellunderstood by those skilled in the art, these quantities (data,selection, retrieval, generation) take the form of electrical, magnetic,or optical signals capable of being stored, transferred, combined, andotherwise manipulated through electrical, optical, and/or biologicalcomponents of a processor and its subsystems.

Various operations will be described as multiple discrete steps in turn,in a manner that is most helpful in understanding the present invention;however, the order of description should not be construed as to implythat these operations are necessarily order dependent.

Various embodiments will be illustrated in terms of exemplary classesand/or objects in an object-oriented programming paradigm. It will beapparent to one skilled in the art that the present invention can bepracticed using any number of different classes/objects, not merelythose included here for illustrative purposes. Furthermore, it will alsobe apparent that the present invention is not limited to any particularsoftware programming language or programming paradigm.

Due to the physical constraints of the acquisition setup, the possibleangular range of the acquisition is often limited. Typically the angularrange 112 is less than 180° in digital breast tomosynthesis (DBT) (seeFIG. 1A). For mathematical reasons, this results in volumetric imageswith a non-isotropic resolution. More precisely, the resolution in theplane perpendicular to the average projection direction is much higher,than the reconstructed resolution in the average direction of the X-Raybeam.

This aspect has to be taken into account when designing viewing methodsfor such images. Given the reconstructed volumetric image, in thefollowing the direction of the lowest resolution will be referred to asthe z-direction, or z. The vectors defining the average detectororientation, i.e. the plane with the highest resolution are denoted asx, and y. The x, y, and z directions are mutually perpendicular to eachother.

In order to display a volumetric image on a standard computer screen,which is two dimensional, a transformation has to be applied in order tocompute a 2-D representation of the volumetric image.

For DBT viewing, a slicing transformation can be used, where a singleslice perpendicular to the z-direction is shown on the screen. Typicallya user interface, such as a slider or text input field, allows the userto select which slice can be shown. In the following this will bereferred to as ‘xy-slicing’ or ‘slicing’. While xy-slicing is animportant viewing tool, it has some limitations. In particular it onlytakes into account a small subset of the information present in thevolumetric data set.

The present invention overcomes the limitation of using only a smallsubset of the information by using a projection method to incorporatethe entirety of the volumetric information. In an embodiment of thepresent invention, time is used as a third dimension to resolveambiguities in a comprehensible and intuitive way.

From the volumetric image a projection can be computed. Let

I: R³→R be the volumetric image.

Let v e R³ be a three dimensional vector defining a first viewingdirection.

Let i_(x) and i_(x) be two vectors spanning a projection planeperpendicular to v and perpendicular to each other.

Then a projection P(v,.) can be defined as follows:

P(v,.): R²→R

P(v,p)=max(I(r)) I r e R³, where v dot i _(x)=p₁, v dot i _(x)=p₂ andP(v,.) is a 2D image that can be displayed on a computer screen usingstandard methods.

Displaying P(v,.) as defined above provides the user with additionaldiagnostic information as it takes into account the whole data set. Forexample if there was a lesion in the examined specimen and thevolumetric image was viewed using xy-slicing then that lesion would onlybe visible in a subset of the slices at or around the z-position of thelesion. If the wrong z-position was chosen, the lesion can be missed.Therefore the user would have to examine each slice to be certain therewas no lesion present, or alternatively risk overlooking a lesion. In anunexpected result, viewing a dynamic comparison in the form of a videocan allow the information to be quickly and efficiently compared.

FIG. 1A shows a specimen 105 imaged from two positions 110, 115 spanningan angular range 112 which generate viewing directions 111, 116respectively. FIG. 1B shows the principle of DBT. In FIG. 1B, thespecimen 105 (e.g. a human breast) can be imaged using an X-Ray sourceand an X-Ray detector from a multitude of positions that lie on the arcbeginning at position 110 and ending at position 115 and which aredetected at detector positions 120 and 125, respectively. The averageacquisition direction is indicated by the dotted line 130. The positionsspan a certain angular range that is defined by the physical constraintsof the machine and the patient's position. The z vector (z) 130 denotesthe middle projection direction in that angular range. FIG. 2illustrates the calculation of a projection P from the volumetric imageI, 235. The projection is defined by the viewing direction v 245, whichdefines the projection plane 240. In general v 245 is not necessarilyidentical to the average acquisition direction z 250. The two vectorsi_(x) 252 and i_(x) 254 are the x-direction and y-direction of theprojection image P, respectively. The vectors i_(x) 252 and i_(x) 254are perpendicular to the viewing direction v 245. The vector i_(x) 252is perpendicular to the vector i_(x) 254, and can be chosen according tothe users viewing preferences or automatically specified according toautomated rules, as described in more detail in “Method and System forRule-Based Display of Sets of Images” issued as U.S. Pat. No. 8,976,190.Digital Imaging and Communication in Medicine (DICOM) parameters formaking rule based decisions include the time of generation of themeasured projection images, the type of tissue measured and whether thetissue has an equivalent control that can be used as a control. Forexample for mediolateral acquisition directions, the y-axis willtypically be chosen such that it aligns with the projection of thepatient's head-foot axis.

Instead, when looking at the projection image P(v,.), an area ofincreased density, such as a lesion or calcification will appear as abrighter spot, irrespective of its z-position, making it possible todetect in many cases. FIG. 7A shows an artists impression of an image ofa human breast computed from a number of 2D X-Ray images produced by aDBT device taken from a specific angle where a micro calcification isoccluded by denser breast tissue. In FIG. 7A a region 774 is identified.FIG. 7B shows an artists impression of an image of a human breast takenfrom a different angle to that shown in FIG. 7A. Comparison of FIG. 7Aand FIG. 7B show a micro calcification is visible in FIG. 7B when thetissue is not occluded by denser breast tissue. Unexpectedly, in FIG. 7Bthe region 774 which was identified in FIG. 7A shows a microcalcification is visible and not occluded by the denser breast tissue.

FIGS. 8A-8D show an artists impression of four (4) images which make uptime points in a mp3 video of a dynamic comparison of DBT of a rightbreast while the viewing direction changes, according to an embodimentof the invention. The mp3 video used to generate FIGS. 8A-8D had aduration of approximately 13 seconds. Unexpectedly, the mp3 video is anexcellent means of inspecting DBTs to identify micro calcifications.FIG. 8A shows the artists impression of a screen dump from the mp3 videoat approximately the two (2) second time point. FIG. 8B shows theartists impression of a screen dump from the mp3 video at approximatelythe five (5) second time point. FIG. 8C shows the artists impression ofa screen dump from the mp3 video at approximately the nine (9) secondtime point. FIG. 8D shows the artists impression of a screen dump fromthe mp3 video at approximately the twelve (12) second time point. Thedynamic comparison illustrates the differences between the intensity ofthe voxel matrix from which the projection image is calculated.Unexpectedly, when viewing the video a spot becomes apparent, which isshown in FIG. 8B and FIG. 8C but is not present in FIG. 8A or FIG. 8D.FIG. 9A shows an enlarged version of FIG. 8B, the artists impression ofthe screen dump from the mp3 video at approximately the five (5) secondtime point where the region 774 is identified. FIG. 9B shows an enlargedversion of FIG. 8C, the artists impression of the screen dump from themp3 video at approximately the nine (9) second time point where theregion 774 is again identified. The spot seen in FIG. 8B (FIG. 9A) andFIG. 8C (FIG. 9B) reduces in intensity between the observation in FIG.8B (FIG. 9A) and the observation in FIG. 8C (FIG. 9B). Unexpectedly, theemergence and dimunition of a relatively bright spot in the sameposition when viewing a video, can also be used to confirm amicrocalcification rather than an artifact of the imaging system. Thus,based on the mp3 video a microcalcification 774 jumps to the viewer'sattention by way of the nature of the dynamic comparison, as shown inthe difference between FIG. 8A where no microcalcification is presentand FIG. 8B (FIG. 9A) where the microcalcification, 774 is present.Viewing the mp3 video improves the visual clarity of identification of amicro calcification.

FIG. 10A shows the image of a human breast generated from a volumetricimage reconstructed from a number of 2D X-Ray images produced by a DBTdevice, where the generated 2-D projection image was formed at aspecific angle, where a micro calcification is occluded by denser breasttissue, as represented in FIG. 7A. FIG. 10B shows the generated 2-Dprojection image of the human breast formed from a different angle tothat shown in FIG. 10A, where the micro calcification is visible and notoccluded by the denser breast tissue, as represented in FIG. 7B. FIGS.11A-11D show four (4) images which make up time points in the mp3 videoof the dynamic comparison of the DBT of the right breast. FIG. 11A showsa screen dump from the mp3 video at a two (2) second time point, asrepresented in FIG. 8A. FIG. 11B shows a screen dump from the mp3 videoat the five (5) second time point, as represented in FIG. 8B. FIG. 11Cshows a screen dump from the mp3 video at the nine (9) second timepoint, as represented in FIG. 8C. FIG. 11D shows a screen dump from themp3 video at the twelve (12) second time point, as represented in FIG.8D. FIG. 12A shows an enlarged version of FIG. 11B, the screen dump fromthe mp3 video at the five (5) second time point where the region 774 isidentified, as represented in FIG. 9A. FIG. 12B shows an enlargedversion of FIG. 11C, the screen dump from the mp3 video at the nine (9)second time point where the region 774 is identified, as represented inFIG. 9B.

A draw-back of any projection method, is that there can be an occlusionor overlay effect. In the case of a maximum intensity projection asdefined above, consider the case where two (2) separate areas ofincreased density are at different z positions on approximately the sameviewing ray v. FIG. 3A shows a specimen 356 with two separate areas 353and 355 of increased density. In the projection they will appear as one,potentially larger spot. That is, for one viewing direction (v1) 358 thetwo separate areas 353 and 355 can be projected to the same spot in theprojection image (projection 1) shown in FIG. 3B.

In an embodiment of the present invention, this ambiguity can beresolved by making the projection dynamic. Instead of choosing a fixedviewing direction v, a dynamic viewing direction can be used. Using analternative viewing direction (v2) 360, the two separate areas 353 and355 project to different spots in the projection image, making itobvious that there are two areas of interest. FIG. 3C shows for thesecond viewing direction (v2) 360 the two separate areas 353 and 355 canbe projected to different spots in the generated 2-D projection image(projection 2).

In an alternative embodiment of the invention, different dynamicfunctions can be used to generate dynamic projection viewing directions.Given the non-isotropy of the input data mentioned above, the mostuseful dynamic functions are continuous periodic functions around the zdirection. Two non-limiting examples of dynamic functions include:

v(t)=normalize( z+A sin(ωt) x )  Equation 1

v(t)=normalize(√{square root over (z)}+A sin(ωt) x+A cos(ωt))  Equation2

where normalize(v)=v/lvl; t: time; ω=2πf; f: frequency of the dynamicmovement and A: Amplitude of the dynamic movement, e.g. A=0.05.

In other embodiments of the invention, different alternative dynamicfunctions can be used to generate dynamic projection viewing directions.In an embodiment of the invention, a linear function can be used inwhich the angle can be changed linearly. In an alternative embodiment ofthe invention, a z direction can be chosen and either the x or the ydirection can be incremented. FIG. 6 illustrates the dynamic variationof the viewing direction v according to Equation 2. The viewingdirection at two different points v_(t1) 666 and v_(t2) 668 at time t₁and t₂ is shown, as well as the corresponding projection planesprojection plane (t₁) 670 and projection plane (t₂) 672. Over time theviewing direction v can be varied around the main acquisition directionz 130.

In another embodiment of the invention, the viewing direction can bedetermined by the user. In another alternative embodiment of theinvention, the viewing direction can be determined by the user with anappropriate input device, such as a mouse. In an embodiment of thepresent invention, let (m_(x1), m_(y1)) be the position of the mouse (orappropriate input device) at a starting time t₁. The starting time canthen be defined by a mouse click (or appropriate input device). In analternative embodiment of the present invention, the starting time canbe triggered by the user entering a certain window with the mouse (orappropriate input device), or other graphical or non graphical criteria.

Assuming the user is moving the mouse, let (m_(x2), m_(y2)) be theposition of the mouse (or appropriate input device) at time t₂. Lets_(width) and s_(height) be the width and height of the screen.

Then v(t2)=normalize ({right arrow over (z)}+2 A x(m_(x2)−m_(x1))/s_(width)+2 A y (m_(y2)−m_(y1))/s_(height)) can be theinteractively controlled viewing direction at time t₂. A person ofordinary skill in the art will appreciate that alternative mappings fromthe mouse coordinates to viewing directions can be used. In variousembodiments of the present invention, alternative input methods ordevices can be used including, a slider, a trackball, a head trackingdevice or an eye tracking device.

The above projection is a maximum intensity projection.

In various other embodiments of the present invention, other projectionfunctions can be used, including emission absorption models or minimumintensity projections. The above projection is equivalent to anorthographic projection, where a 3-D object is represented in twodimensions through parallel projection, where all the projection linesare orthogonal to the projection plane. A person of ordinary skill inthe art will appreciate that alternative projections includingperspective projections can be used.

In an embodiment of the invention, an optimal viewing direction can beselected by comparing the resulting projection images at a plurality ofviewing directions. In an embodiment of the invention, the criterionused for determining the optimal viewing direction can be a viewingdirection that identifies an unobserved obstruction. In an alternativeembodiment of the invention, the criterion used for determining theoptimal viewing direction can be a viewing direction that improves thevisual clarity of an initial projection image. In another alternativeembodiment of the invention, the criterion used for determining theoptimal viewing direction can be a viewing direction that improves thevisual clarity of an improved projection image compared with an initialprojected image. In a different embodiment of the invention, thecriterion used for determining the optimal viewing direction can be aviewing direction that improves the visual clarity of identification ofan obstruction. In another different embodiment of the invention, thecriterion used for determining the optimal viewing direction can be aviewing direction that identifies an obstruction using directcomparison. In another embodiment of the invention, the criterion usedfor determining the optimal viewing direction can be a viewing directionthat improves the direct comparison clarity of an initial projectionimage. In an embodiment of the invention, the criterion used fordetermining the optimal viewing direction can be a viewing directionthat improves the direct comparison clarity of an improved projectionimage compared with an initial projected image. In another embodiment ofthe invention, the criterion used for determining the optimal viewingdirection can be a viewing direction that improves the direct comparisonclarity of identification of an obstruction.

Volumetric images in DBT are quite large data sets, as the xy-resolutionis an order of magnitude larger than for example a standard CT scan. Inorder to render such large images at interactive speeds graphicsprocessing units (GPU) can be utilized, see for example Methods andApparatus for Visualizing Three-Dimensional and Higher-Dimensional ImageData Sets, U.S. Pat. No. 8,189,002, which is herein expresslyincorporated by reference in its entirety. In typical DBT images, only asubset of the voxels of the volumetric image contain tissue, while othervoxels are background pixels that are irrelevant for the diagnosis. Inan embodiment of the present invention, by using a thresholdsegmentation these background pixels can be identified. FIG. 4 shows howonly a subset of the acquisition volume is covered by the specimen 462,while other areas (hatched) 464 only contain background pixels. Thesebackground pixels can be identified using threshold segmentation. FIG. 5shows the volume can be subdivided into sub-volumes. In one embodimentof the invention, an octree decomposition scheme can be used for thissubdivision. In another embodiment of the invention, a binary spacepartitioning (BSP) scheme can be used for the subdivision. A person withordinary skills in the art will appreciate that other subdivisionschemes can be used. Sub-volumes that contain only background voxels(shown as hatched in FIG. 4 and FIG. 5) 464 can be skipped during therendering process. Sub-volumes 463 that contain both, background voxelsand tissue voxels can be further sub-divided until a configured minimumsize containing specimen 462 or background 464 can be reached. In anembodiment of the invention, bricking can be used to display only thosesub-volumes that are not background-only. The technique of bricking forGPU based rendering is described in U.S. Pat. No. 8,189,002.

In an embodiment of the present invention, for the effective use ofdynamic projection images, a sufficiently high frame rate is required inorder to allow for a smooth rendering that appears natural to the user.This can be achieved in many cases by using GPU hardware combined withthe bricking technique.

In an alternative embodiment of the present invention, a periodicdynamic viewing direction function can be used, and a sequence ofprojections covering one full period (1/f) can be pre-rendered, and thenbe played back in a loop. In case of a client server visualizationsystem, the pre-rendered images can be computed on the server side andcached on the client side thereby making optimal use of the bandwidthand allowing for smooth playback even on slow networks.

In radiological diagnostics, comparison to prior images is relevant todetect change, e.g. tumor growth. In an embodiment of the presentinvention, a projection of a current image and a projection of acorresponding prior image can be displayed side-by-side and used todetermine the change in tumor characteristics. The comparison caninclude the user visually comparing with the naked eye. The comparisoncan also be undertaken by a direct comparison program where equivalentviewing directions are used for the direct comparison. In variousembodiments of the present invention, the user can choose the samedynamic viewing direction function for both, the current and the priorimage, thereby allowing for direct comparison.

Another aspect of the invention is to combine the projection display ofthe volumetric image with conventional 2D mammograms or other X-Ray orradiological images, by dividing the available computer screens intovirtual view ports and using one or more of the virtual view ports todisplay the one or more projection images, and one or more of thevirtual viewports to display the other radiological images.

A method for displaying one or more optimal projection images generatedfrom a volumetric image comprising the steps of receiving the volumetricimage, computing a plurality of projection images of the volumetricimage using a plurality of viewing directions, where at least an initialprojection image of the plurality of projection images is computed usinga first viewing direction, where a second viewing direction of theplurality of viewing directions is not equal to the first viewingdirection, one or more of time comparing, structurally comparing anddynamically comparing the plurality of projection images to determineone or more optimal projection images and displaying the optimalprojection images.

A method for identifying one or more optimal projection images generatedfrom a volumetric image comprising the steps of receiving the volumetricimage, computing a plurality of projection images of the volumetricimage using a plurality of viewing directions, where at least an initialprojection image of the plurality of projection images is computed usinga first viewing direction, where a second viewing direction of theplurality of viewing directions is not equal to the first viewingdirection, and one or more of time comparing, structurally comparing anddynamically comparing the plurality of projection images to determineone or more optimal projection images.

A method for identifying one or more optimal projection images generatedfrom a volumetric image comprising the steps of receiving the volumetricimage, computing a plurality of projection images of the volumetricimage using a plurality of viewing directions, where at least an initialprojection image of the plurality of projection images is computed usinga first viewing direction, where a second viewing direction of theplurality of viewing directions is not equal to the first viewingdirection, and one or more of time comparing, structurally comparing anddynamically comparing the plurality of projection images to determineone or more optimal projection images, where the optimal viewingdirection is selected from the group consisting of a viewing directionthat identifies an unobserved obstruction, a viewing direction thatimproves the visual clarity of the first projection image, a viewingdirection that improves the visual clarity of the second projectionimage, a viewing direction that improves the visual clarity ofidentification of an obstruction, a viewing direction that identifies anobstruction using direct comparison, a viewing direction that increasesthe differentiated intensity values of the first projection image, aviewing direction that increases the differentiated intensity values ofthe second projection image, a viewing direction that improves thedirect comparison clarity of the first projection image, a viewingdirection that improves the direct comparison clarity of the secondprojection image, and a viewing direction that improves the directcomparison clarity of identification of an obstruction.

A method to determine one or more optimal projection images from avolumetric image comprising the steps of receiving a volumetric image,computing a plurality of projection images based on the volumetric imageusing a plurality of viewing directions, one or more of time comparing,structurally comparing and dynamically comparing the plurality ofprojection images to determine one or more optimal viewing directions,and correlating the optimal viewing directions with one or moreprojection images of the plurality of projection images to determine oneor more optimal projection images.

A method to determine one or more optimal projection images from avolumetric image comprising the steps of receiving a volumetric image,computing a plurality of projection images based on the volumetric imageusing a plurality of viewing directions, one or more of time comparing,structurally comparing and dynamically comparing the plurality ofprojection images to determine one or more optimal viewing directions,and correlating the optimal viewing directions with one or moreprojection images of the plurality of projection images to determine oneor more optimal projection images, where the optimal viewing directionis selected from the group consisting of a viewing direction thatidentifies an unobserved obstruction, a viewing direction that improvesthe visual clarity of the first projection image, a viewing directionthat improves the visual clarity of the second projection image, aviewing direction that improves the visual clarity of identification ofan obstruction, a viewing direction that identifies an obstruction usingdirect comparison, a viewing direction that improves the directcomparison clarity of the first projection image, a viewing directionthat improves the direct comparison clarity of the second projectionimage, and a viewing direction that improves the direct comparisonclarity of identification of an obstruction.

A method to determine one or more optimal projection images from avolumetric image comprising the steps of receiving a volumetric image,computing a plurality of projection images based on the volumetric imageusing a plurality of viewing directions, one or more of time comparing,structurally comparing and dynamically comparing the plurality ofprojection images to determine one or more optimal viewing directions,and correlating the optimal viewing directions with one or moreprojection images of the plurality of projection images to determine oneor more optimal projection images, where the volumetric image is a 3Dimage.

A method to determine one or more optimal projection images from avolumetric image comprising the steps of receiving a volumetric image,computing a plurality of projection images based on the volumetric imageusing a plurality of viewing directions, one or more of time comparing,structurally comparing and dynamically comparing the plurality ofprojection images to determine one or more optimal viewing directions,and correlating the optimal viewing directions with one or moreprojection images of the plurality of projection images to determine oneor more optimal projection images, where the plurality of projectionimages are 2D images.

A method to determine one or more optimal projection images from avolumetric image comprising the steps of receiving a volumetric image,computing a plurality of projection images based on the volumetric imageusing a plurality of viewing directions, one or more of time comparing,structurally comparing and dynamically comparing the plurality ofprojection images to determine one or more optimal viewing directions,and correlating the optimal viewing directions with one or moreprojection images of the plurality of projection images to determine oneor more optimal projection images, where at least one of the pluralityof viewing directions is determined using a periodic continuousmathematical function.

A method to determine one or more optimal projection images from avolumetric image comprising the steps of receiving a volumetric image,computing a plurality of projection images based on the volumetric imageusing a plurality of viewing directions, one or more of time comparing,structurally comparing and dynamically comparing the plurality ofprojection images to determine one or more optimal viewing directions,and correlating the optimal viewing directions with one or moreprojection images of the plurality of projection images to determine oneor more optimal projection images, where at least one of the pluralityof viewing directions is determined using a periodic continuousmathematical function, where the plurality of projection images is asequence of projections images spanning one period of the periodiccontinuous mathematical function.

A method to determine one or more optimal projection images from avolumetric image comprising the steps of receiving a volumetric image,computing a plurality of projection images based on the volumetric imageusing a plurality of viewing directions, one or more of time comparing,structurally comparing and dynamically comparing the plurality ofprojection images to determine one or more optimal viewing directions,and correlating the optimal viewing directions with one or moreprojection images of the plurality of projection images to determine oneor more optimal projection images, where at least one of the pluralityof viewing directions is determined using a periodic continuousmathematical function, where the plurality of projection images is asequence of projections images spanning one period of the periodiccontinuous mathematical function, further comprising rendering andcaching a sequence of projection images.

A method to determine one or more optimal projection images from avolumetric image comprising the steps of receiving a volumetric image,computing a plurality of projection images based on the volumetric imageusing a plurality of viewing directions, one or more of time comparing,structurally comparing and dynamically comparing the plurality ofprojection images to determine one or more optimal viewing directions,and correlating the optimal viewing directions with one or moreprojection images of the plurality of projection images to determine oneor more optimal projection images, where at least one of the pluralityof viewing directions is determined using a periodic continuousmathematical function, where the plurality of projection images is asequence of projections images spanning one period of the periodiccontinuous mathematical function, further comprising rendering andcaching a sequence of projection images, where the rendered and cachedsequence of projections are played back one or more times.

A method to determine one or more optimal projection images from avolumetric image comprising the steps of receiving a volumetric image,computing a plurality of projection images based on the volumetric imageusing a plurality of viewing directions, one or more of time comparing,structurally comparing and dynamically comparing the plurality ofprojection images to determine one or more optimal viewing directions,and correlating the optimal viewing directions with one or moreprojection images of the plurality of projection images to determine oneor more optimal projection images, where at least one of the pluralityof viewing directions is determined using a periodic continuousmathematical function, where the plurality of projection images is asequence of projections images spanning one period of the periodiccontinuous mathematical function, further comprising rendering andcaching a sequence of projection images, where the rendering is carriedout on a server and one or both the caching and play back is carried outon a client computer.

A method to determine one or more optimal projection images from avolumetric image comprising the steps of receiving a volumetric image,computing a plurality of projection images based on the volumetric imageusing a plurality of viewing directions, one or more of time comparing,structurally comparing and dynamically comparing the plurality ofprojection images to determine one or more optimal viewing directions,and correlating the optimal viewing directions with one or moreprojection images of the plurality of projection images to determine oneor more optimal projection images, where a graphics processing unit isused to compute one or more of the plurality of projection images.

A method to determine one or more optimal projection images from avolumetric image comprising the steps of receiving a volumetric image,computing a plurality of projection images based on the volumetric imageusing a plurality of viewing directions, one or more of time comparing,structurally comparing and dynamically comparing the plurality ofprojection images to determine one or more optimal viewing directions,and correlating the optimal viewing directions with one or moreprojection images of the plurality of projection images to determine oneor more optimal projection images, where a graphics processing unit isused to compute one or more of the plurality of projection images, wherebricking is used to accelerate computation of one or more of theplurality of projection images.

A method to determine one or more optimal projection images from avolumetric image comprising the steps of receiving a volumetric image,computing a plurality of projection images based on the volumetric imageusing a plurality of viewing directions, one or more of time comparing,structurally comparing and dynamically comparing the plurality ofprojection images to determine one or more optimal viewing directions,and correlating the optimal viewing directions with one or moreprojection images of the plurality of projection images to determine oneor more optimal projection images, where one or more of the plurality ofviewing directions is based on user input.

A method to determine one or more optimal projection images from avolumetric image comprising the steps of receiving a volumetric image,computing a plurality of projection images based on the volumetric imageusing a plurality of viewing directions, one or more of time comparing,structurally comparing and dynamically comparing the plurality ofprojection images to determine one or more optimal viewing directions,and correlating the optimal viewing directions with one or moreprojection images of the plurality of projection images to determine oneor more optimal projection images, further comprising visually comparingthe plurality of projection images.

A system that displays a first projection image and a second projectionimage of a volumetric image comprising computing a first projectionimage of the volumetric image using a first viewing direction, computinga second projection image of the volumetric image using a second viewingdirection, where the first viewing direction is not equal to the secondviewing direction, and displaying the first projection image and thesecond projection image.

A system that displays a first projection image and a second projectionimage of a volumetric image comprising computing a first projectionimage of the volumetric image using a first viewing direction, computinga second projection image of the volumetric image using a second viewingdirection, where the first viewing direction is not equal to the secondviewing direction, and displaying the first projection image and thesecond projection image, further comprising computing a third projectionimage using a third viewing direction, and displaying one or both thefirst projection image and the second projection image with the thirdprojection image.

A system that displays a first projection image and a second projectionimage of a volumetric image comprising computing a first projectionimage of the volumetric image using a first viewing direction, computinga second projection image of the volumetric image using a second viewingdirection, where the first viewing direction is not equal to the secondviewing direction, and displaying the first projection image and thesecond projection image, further comprising computing a third projectionimage using a third viewing direction, and displaying one or both thefirst projection image and the second projection image with the thirdprojection image, where one or both the second viewing direction and thethird viewing direction are determined using a periodic continuousmathematical function.

A system that compares a first projection image and a second projectionimage of a volumetric image comprising computing a first projectionimage of the volumetric image using a first viewing direction, computinga second projection image of the volumetric image using a second viewingdirection, and one or more of time comparing, structurally comparing anddynamically comparing the first projection image and the secondprojection image.

A system that compares a first projection image and a second projectionimage of a volumetric image comprising computing a first projectionimage of the volumetric image using a first viewing direction, computinga second projection image of the volumetric image using a second viewingdirection, and one or more of time comparing, structurally comparing anddynamically comparing the first projection image and the secondprojection image, further comprising computing a third projection imageusing a third viewing direction, and comparing one or both the firstprojection image and the second projection image with the thirdprojection image.

A system that compares a first projection image and a second projectionimage of a volumetric image comprising computing a first projectionimage of the volumetric image using a first viewing direction, computinga second projection image of the volumetric image using a second viewingdirection, and one or more of time comparing, structurally comparing anddynamically comparing the first projection image and the secondprojection image, further comprising computing a third projection imageusing a third viewing direction, and comparing one or both the firstprojection image and the second projection image with the thirdprojection image, where one or both the second viewing direction and thethird viewing direction are determined using a periodic continuousmathematical function.

A method for identifying an object in a projection image comprising thesteps of receiving a three dimensional volumetric image of a tissue,computing a plurality of projection images of the three dimensionalvolumetric image of the tissue using a plurality of viewing directions,one or more of time comparing, structurally comparing and dynamicallycomparing the plurality of projection images, and identifying an objectthat is present in a projection image selected from the plurality ofprojection images that is not present in one or more of the one or moreprojection images selected from the plurality of projection images.

A method for identifying an object in a projection image comprising thesteps of receiving a three dimensional volumetric image of a tissue,computing a plurality of projection images of the three dimensionalvolumetric image of the tissue using a plurality of viewing directions,one or more of time comparing, structurally comparing and dynamicallycomparing the plurality of projection images, and identifying an objectthat is present in a projection image selected from the plurality ofprojection images that is not present in one or more of the one or moreprojection images selected from the plurality of projection images,where at least one of the plurality of viewing directions is determinedusing a periodic continuous mathematical function.

A method for identifying an object in a projection image comprising thesteps of receiving a three dimensional volumetric image of a tissue,computing a plurality of projection images of the three dimensionalvolumetric image of the tissue using a plurality of viewing directions,one or more of time comparing, structurally comparing and dynamicallycomparing the plurality of projection images, and identifying an objectthat is present in a projection image selected from the plurality ofprojection images that is not present in one or more of the one or moreprojection images selected from the plurality of projection images,where at least one of the plurality of viewing directions is determinedusing a periodic continuous mathematical function, where the pluralityof projection images is a sequence of projection images spanning oneperiod of the periodic continuous mathematical function.

A method for identifying an object in a projection image comprising thesteps of receiving a three dimensional volumetric image of a tissue,computing a plurality of projection images of the three dimensionalvolumetric image of the tissue using a plurality of viewing directions,one or more of time comparing, structurally comparing and dynamicallycomparing the plurality of projection images, and identifying an objectthat is present in a projection image selected from the plurality ofprojection images that is not present in one or more of the one or moreprojection images selected from the plurality of projection images,where at least one of the plurality of viewing directions is determinedusing a periodic continuous mathematical function, where the pluralityof projection images is a sequence of projection images spanning oneperiod of the periodic continuous mathematical function, furthercomprising rendering and caching a sequence of projection images.

A method for identifying an object in a projection image comprising thesteps of receiving a three dimensional volumetric image of a tissue,computing a plurality of projection images of the three dimensionalvolumetric image of the tissue using a plurality of viewing directions,one or more of time comparing, structurally comparing and dynamicallycomparing the plurality of projection images, and identifying an objectthat is present in a projection image selected from the plurality ofprojection images that is not present in one or more of the one or moreprojection images selected from the plurality of projection images,where at least one of the plurality of viewing directions is determinedusing a periodic continuous mathematical function, where the pluralityof projection images is a sequence of projection images spanning oneperiod of the periodic continuous mathematical function, furthercomprising rendering and caching a sequence of projection images, wherethe rendered and cached sequence of projection images are played backone or more times.

A method for identifying an object in a projection image comprising thesteps of receiving a three dimensional volumetric image of a tissue,computing a plurality of projection images of the three dimensionalvolumetric image of the tissue using a plurality of viewing directions,one or more of time comparing, structurally comparing and dynamicallycomparing the plurality of projection images, and identifying an objectthat is present in a projection image selected from the plurality ofprojection images that is not present in one or more of the one or moreprojection images selected from the plurality of projection images,where at least one of the plurality of viewing directions is determinedusing a periodic continuous mathematical function, where the pluralityof projection images is a sequence of projection images spanning oneperiod of the periodic continuous mathematical function, furthercomprising rendering and caching a sequence of projection images, wherethe rendering is carried out on a server.

A method for identifying an object in a projection image comprising thesteps of receiving a three dimensional volumetric image of a tissue,computing a plurality of projection images of the three dimensionalvolumetric image of the tissue using a plurality of viewing directions,one or more of time comparing, structurally comparing and dynamicallycomparing the plurality of projection images, and identifying an objectthat is present in a projection image selected from the plurality ofprojection images that is not present in one or more of the one or moreprojection images selected from the plurality of projection images,where at least one of the plurality of viewing directions is determinedusing a periodic continuous mathematical function, where the pluralityof projection images is a sequence of projection images spanning oneperiod of the periodic continuous mathematical function, furthercomprising rendering and caching a sequence of projection images, wherethe caching is carried out on a client computer.

A method for identifying an object in a projection image comprising thesteps of receiving a three dimensional volumetric image of a tissue,computing a plurality of projection images of the three dimensionalvolumetric image of the tissue using a plurality of viewing directions,one or more of time comparing, structurally comparing and dynamicallycomparing the plurality of projection images, and identifying an objectthat is present in a projection image selected from the plurality ofprojection images that is not present in one or more of the one or moreprojection images selected from the plurality of projection images,where at least one of the plurality of viewing directions is determinedusing a periodic continuous mathematical function, where the pluralityof projection images is a sequence of projection images spanning oneperiod of the periodic continuous mathematical function, furthercomprising rendering and caching a sequence of projection images, wherethe rendering is carried out on a server, where the play back is carriedout on a client computer.

A method for identifying an object in a projection image comprising thesteps of receiving a three dimensional volumetric image of a tissue,computing a plurality of projection images of the three dimensionalvolumetric image of the tissue using a plurality of viewing directions,one or more of time comparing, structurally comparing and dynamicallycomparing the plurality of projection images, and identifying an objectthat is present in a projection image selected from the plurality ofprojection images that is not present in one or more of the one or moreprojection images selected from the plurality of projection images,where at least one of the plurality of viewing directions is determinedusing a periodic continuous mathematical function, where a graphicsprocessing unit is used to compute one or more of the plurality ofprojection images.

A method for identifying an object in a projection image comprising thesteps of receiving a three dimensional volumetric image of a tissue,computing a plurality of projection images of the three dimensionalvolumetric image of the tissue using a plurality of viewing directions,one or more of time comparing, structurally comparing and dynamicallycomparing the plurality of projection images, and identifying an objectthat is present in a projection image selected from the plurality ofprojection images that is not present in one or more of the one or moreprojection images selected from the plurality of projection images,where at least one of the plurality of viewing directions is determinedusing a periodic continuous mathematical function, where a graphicsprocessing unit is used to compute one or more of the plurality ofprojection images, where bricking is used to accelerate computation ofone or more of the plurality of projection images.

A method for identifying an optimal projection image comprising thesteps of receiving a volumetric image, computing the plurality ofprojection images based on the volumetric image using a plurality ofviewing directions, and comparing the plurality of projection images todetermine an optimal viewing direction corresponding to an optimalprojection image.

A method for identifying an optimal projection image comprising thesteps of receiving a volumetric image, computing the plurality ofprojection images based on the volumetric image using a plurality ofviewing directions, and comparing the plurality of projection images todetermine an optimal viewing direction corresponding to an optimalprojection image, where the optimal viewing direction is selected fromthe group consisting of a viewing direction that identifies anunobserved obstruction, a viewing direction that improves the visualclarity of the first projection image, a viewing direction that improvesthe visual clarity of the second projection image, a viewing directionthat improves the visual clarity of identification of an obstruction, aviewing direction that identifies an obstruction using directcomparison, a viewing direction that improves the direct comparisonclarity of the first projection image, a viewing direction that improvesthe direct comparison clarity of the second projection image, and aviewing direction that improves the direct comparison clarity ofidentification of an obstruction.

A method for displaying a plurality of projection images comprising thesteps of receiving a volumetric image, computing the plurality ofprojection images based on the volumetric image using a plurality ofviewing directions and displaying the plurality of projection images.

A method for comparing a first projection image and a second projectionimage comprising the steps of receiving a volumetric image, computingthe first projection image based on the volumetric image using a firstviewing direction, computing the second projection image based on thevolumetric image using a second viewing direction, where the firstviewing direction is not equal to the second viewing direction and oneor more of time comparing, structurally comparing and dynamicallycomparing the first projection image and the second projection image.

A method for comparing a first projection image and a second projectionimage comprising the steps of receiving a volumetric image, computingthe first projection image based on the volumetric image using a firstviewing direction, computing the second projection image based on thevolumetric image using a second viewing direction, where the firstviewing direction is not equal to the second viewing direction and oneor more of time comparing, structurally comparing and dynamicallycomparing the first projection image and the second projection image,further comprising one or more steps selected from the group consistingof identifying visually an obstruction, improving the visual clarity ofthe first projection image, improving the visual clarity of the secondprojection image, improving the visual clarity of identification of anobstruction, identifying an obstruction using direct comparison,improving the direct comparison clarity of the first projection image,improving the direct comparison clarity of the second projection image,and improving the direct comparison clarity of identification of anobstruction.

A method for displaying one or more unobstructed projection imagescomprising the steps of receiving a volumetric image, computing aplurality of projection images based on the volumetric image using aplurality of viewing directions, where at least a first projection imageof the plurality of projection images is computed using a first viewingdirection and at least a second projection image of the plurality ofprojection images is computed using a second viewing direction, wherethe first viewing direction is not equal to the second viewingdirection, one or more of time comparing, structurally comparing anddynamically comparing the first projection image and the secondprojection image to determine if one or both of the first projectionimage and the second projection image are unobstructed, and displayingbased on the comparison one or both the first projection image and thesecond projection image.

A method for displaying an unobstructed projection image of a breastcomprising the steps of receiving a volumetric image of the breast,computing a first projection image of the breast based on the volumetricimage using a first viewing direction and a second projection image ofthe breast based on the volumetric image using a second viewingdirection, where the first viewing direction is not equal to the secondviewing direction, one or more of time comparing, structurally comparingand dynamically comparing the second projection image of the breast withthe first projection image of the breast to determine if one or both thefirst projection image of the breast and second projection image of thebreast is unobstructed, and based on the comparison displaying one orboth the first projection image of the breast and second projectionimage of the breast.

A system for displaying unobstructed breast projection images comprisingreceiving a plurality of volumetric images of a breast, where a firstvolumetric image of the plurality of projection images is measured at afirst time and a second volumetric image of the plurality of projectionimages is measured at a second time, where the first time differs fromthe second time by a time interval, computing a first projection imagefrom the first volumetric image measured at the first time using a firstviewing direction, computing one or more projection images from thefirst volumetric image measured at the first time using one or moreviewing directions, one or more of time comparing, structurallycomparing and dynamically comparing the first projection image and theone or more projection images to determine an unobstructed viewingdirection, where a second projection image corresponds with the one ormore projection images at the unobstructed viewing direction, computinga third projection image from the second volumetric image measured atthe second time using the unobstructed viewing direction, and displayingthe second projection image and the third projection image.

A system for displaying unobstructed breast projection images comprisingreceiving a plurality of volumetric images of a breast, where a firstvolumetric image of the plurality of projection images is measured at afirst time and a second volumetric image of the plurality of projectionimages is measured at a second time, where the first time differs fromthe second time by a time interval, computing a first projection imagefrom the first volumetric image measured at the first time using a firstviewing direction, computing one or more projection images from thefirst volumetric image measured at the first time using one or moreviewing directions, one or more of time comparing, structurallycomparing and dynamically comparing the first projection image and theone or more projection images to determine an unobstructed viewingdirection, where a second projection image corresponds with the one ormore projection images at the unobstructed viewing direction, computinga third projection image from the second volumetric image measured atthe second time using the unobstructed viewing direction, and displayingthe second projection image and the third projection image, furthercomprising computing a fourth projection image from the secondvolumetric image measured at the second time using the first viewingdirection.

A method for identifying additional lesions in a tissue comprising thesteps of computing a plurality of projection images of the tissue usinga plurality of viewing directions, where a first projection image iscomputed using a first viewing direction and a second projection imageis computed using a second viewing direction, displaying the firstprojection image and the second projection image, one or more of timecomparing, structurally comparing and dynamically comparing the firstprojection image and the second projection image, visually identifyingan intense spot that separates in the second projection image from thefirst projection image.

A system that displays a first projection image and a second projectionimage of a volumetric image comprising a processor responsive to acommand to select a volumetric image one or more digital data processorscapable of carrying out the steps including, computing a firstprojection image of the volumetric image using a first viewingdirection, computing a second projection image of the volumetric imageusing a second viewing direction, and graphics resources for displayingthe first projection image and the second projection image.

A system that compares a first projection image and a second projectionimage of a volumetric image comprising a processor responsive to acommand to select a volumetric image, one or more digital dataprocessors capable of carrying out the steps including computing a firstprojection image of the volumetric image using a first viewingdirection, computing a second projection image of the volumetric imageusing a second viewing direction, and graphics resources for comparingthe first projection image and the second projection image.

A method for displaying one or more unobstructed projection imagescomprising the steps of receiving a volumetric image, computing aplurality of projection images based on the volumetric image using aplurality of viewing directions, where at least a first projection imageof the plurality of projection images is computed using a first viewingdirection and at least a second projection image of the plurality ofprojection images is computed using a second viewing direction, wherethe first viewing direction is not equal to the second viewingdirection, one or more of time comparing, structurally comparing anddynamically comparing the first projection image and the secondprojection image to determine if one or both of the first projectionimage and the second projection image are unobstructed, and displayingbased on the comparison one or both the first projection image and thesecond projection image.

A method of visualizing a dynamic comparison of a volumetric imagecomprising the steps of receiving the volumetric image, computing aplurality of projection images of the volumetric image using a pluralityof viewing directions between a smallest viewing direction and a largestviewing direction, and displaying a video showing the plurality ofprojection images, where the viewing direction changes with time.

The term ‘brick’ or ‘bricking’ means partitioning a 3D image or aportion of the 3D image. Bricking is an iterative process involvingdetermining the intensity of pixels in the 2D image based on the rulethat all points in the 3D image data that are required for evaluatingthe intensities of the sample points along a ray passing through a brickare located within that brick. That is in an imaging apparatus having aCPU and a GPU with a plurality of programmable vertex shaders coupled toa plurality of programmable pixel shaders, the CPU partitions the 3Dimage into a plurality ‘bricks’ based on the vertex shaders and pixelshaders determining the intensities of one or more pixels in the 2Dimage as an iterative function of intensities of sample points in one ormore bricks in the 3D image through which viewing rays associated withthose pixels are passed, and where any two adjacent bricks preferablyhave a sufficient overlap such that all points in the 3D image data thatare required for evaluating the intensities of the sample points along aray passing through a brick are located within that brick.

The term ‘view’ or ‘viewing’ means a display of a 3D or 2D image.

The phrases ‘viewing position’ or ‘viewing ray’ refer to a display of a3D or 2D image as observed from the viewing position or along a linedefined by the viewing ray.

The term ‘microcalcification’ refers to small deposits of calciumtypically seen in a breast mammogram which depending on shape, number,pattern and/or relative position can be used as an early and/orpresenting sign of breast cancer.

The term ‘obstruction’ means a filling defect or other ductalabnormality, such as ductal ectasia, fibrocystic changes or a ductalirregularity such as can be observed with ductography of the breastincluding galactography and ductogalactography.

The foregoing description of embodiments of the methods, systems, andcomponents of the present invention has been provided for the purposesof illustration and description. It is not intended to be exhaustive orto limit the invention to the precise forms disclosed. Manymodifications and variations will be apparent to one of ordinary skillin the relevant arts. For example, steps performed in the embodiments ofthe invention disclosed can be performed in alternate orders, certainsteps can be omitted, and additional steps can be added. The embodimentswere chosen and described in order to best explain the principles of theinvention and its practical application, thereby enabling others skilledin the art to understand the invention for various embodiments and withvarious modifications that are suited to the particular usedcontemplated. Other embodiments are possible and are covered by theinvention. Such embodiments will be apparent to persons skilled in therelevant art(s) based on the teachings contained herein. The breadth andscope of the present invention should not be limited by any of theabove-described exemplary embodiments, but should be defined only inaccordance with the following claims and their equivalents. Theinvention is illustrated by way of example and not by way of limitationin the figures of the accompanying drawings in which like referencesindicate similar elements. It should be noted that references to ‘an’ or‘one’ embodiment in this disclosure are not necessarily to the sameembodiment, and such references mean at least one.

What is claimed:
 1. A method comprising the steps of: providing a servercomputer including a graphics processing unit and a first memory, wherethe server computer: a) receives a 3-D volumetric image reconstructedfrom a plurality of measured 2-D projection images; b) computes three ormore generated 2-D projection images based on three or more 3-Dvolumetric image viewing directions, where a first viewing directiongenerated by a first straight line drawn between a first position and anobject is used to compute a first generated 2-D projection image, wherethe angle between the first straight line and the first viewingdirection is given by θ₀, where θ₀ is equal to zero, a second viewingdirection generated by a second straight line drawn between a secondposition and the object is used to compute a second generated 2-Dprojection image, where the angle between the second straight line andthe first viewing direction is given by θ₁, and at least a third viewingdirection generated by a straight line drawn between a third positionand the object is used to compute a third generated 2-D projectionimage, where the angle between the third straight line and the firstviewing direction is θ₂; and c) sends the three or more generated 2-Dprojection images and viewing instructions to a remote device whichincludes a graphics display unit and a second memory, where the three ormore generated 2-D projection images are stored in the second memory,where the viewing instructions determine that the three or moregenerated 2-D projection images are displayed on the graphics displayunit in time delay corresponding with one or both increasing anddecreasing θ.
 2. The method of claim 1, where at least one generated 2-Dprojection images of the three or more generated 2-D projection imagesis selected from the group consisting of a generated 2-D projectionimage that identifies: i) a microcalcification; ii) an obstruction; iii)a microcalcification includes two or more microcalcifications; iv) anobstruction includes a microcalcification and an obstruction; v) anobstruction includes two or more obstructions; vi) a microcalcificationusing direct comparison; and vii) an obstruction using directcomparison.
 3. The method of claim 1, where at least one generated 2-Dprojection images of the three or more generated 2-D projection imagesis selected from the group consisting of a generated 2-D projectionimage that improves: i) identification of the first generated 2-Dprojection image; ii) identification of the second generated 2-Dprojection image; iii) identification of a microcalcification; iv)identification of an obstruction; v) resolution of twomicrocalcifications; vi) resolution of a microcalcification and anobstruction; vii) resolution of two obstructions; viii) directcomparison with the first generated 2-D projection image; ix) directcomparison with the second generated 2-D projection image; x) directcomparison of a microcalcification; and xi) direct comparison of anobstruction.
 4. The method of claim 1, where the 3-D volumetric image isa Digital Breast Tomosynthesis image.
 5. The method of claim 1, wherethe three or more generated 2-D projection images are displayed as avideo.
 6. The method of claim 5, where the video displays a dynamiccomparison.
 7. The method of claim 1, where the viewing directions areselected according to a periodic continuous mathematical function. 8.The method of claim 7, where the three or more generated 2-D projectionimages are generated from viewing directions spanning one period of theperiodic continuous mathematical function.
 9. The method of claim 1,further comprising receiving one or more rendered generated 2-Dprojection images.
 10. The method of claim 9, where the rendering iscarried out on a server.
 11. The method of claim 1, where one or boththe first memory and the second memory is a cache.
 12. The method ofclaim 11, further comprising storing the viewing instructions in cache.13. The method of claim 11, further comprising using the viewinginstructions to format the three or more generated 2-D projection imagesas a video.
 14. The method of claim 11, further comprising storing theviewing instructions in the second memory as an executable file todisplay the three or more generated 2-D projection images as a video.15. A method comprising the steps of: providing a server computerincluding a graphics processing unit and a first memory, where theserver computer: a) receives a first 3-D volumetric image of a firsttissue measured at a first time of measurement; b) computes a pluralityof generated 2-D projection images of the first 3-D volumetric imageusing a plurality of viewing directions; c) compares the plurality ofgenerated 2-D projection images to identify a first viewing directionthat identifies an obstruction, where the first viewing directioncorresponds with a first generated 2-D projection image; d) receiving asecond 3-D volumetric image, where the second 3-D volumetric image isselected from the group consisting of: (i) a second 3-D volumetric imageof the first tissue measured before the first time of measurement; (ii)a second 3-D volumetric image of the first tissue measured after thefirst time of measurement, (iii) a second 3-D volumetric image of asecond tissue measured at the first time of measurement, where thesecond 3-D volumetric image of the second tissue enables a structuralcomparison of the first 3-D volumetric image of first tissue; (iv) asecond 3-D volumetric image of a second tissue measured before the firsttime of measurement, where the second 3-D volumetric image of the secondtissue enables a structural comparison with the first 3-D volumetricimage of first tissue; and (v) a second 3-D volumetric image of a secondtissue measured after the first time of measurement, where the second3-D volumetric image of the second tissue enables a structuralcomparison with the first 3-D volumetric image of first tissue; and e)using an equivalent viewing direction to compute a second generated 2-Dprojection image; and f) sending the first generated 2-D projectionimage, the second generated 2-D projection image and viewinginstructions to a remote display device which includes a graphicsdisplay unit and a second memory, where the first generated 2-Dprojection image, the second generated 2-D projection image and viewinginstructions are stored on the second memory, where the viewinginstructions determine the orientation of the second generated 2-Dprojection image with respect to the first generated 2-D projectionimage, when the first generated 2-D projection image and the secondgenerated 2-D projection image are displayed on the graphics displayunit.
 16. The method of claim 15, where the first generated 2-Dprojection image is selected from the group consisting of the pluralityof generated 2-D projection images such that it identifies: i) amicrocalcification; ii) a microcalcification using direct comparison;and iii) an obstruction using direct comparison.
 17. The method of claim15, where the first generated 2-D projection image is selected from thegroup consisting of the plurality of generated 2-D projection imagessuch that it improves: i) visual clarity of the first generated 2-Dprojection image; ii) visual clarity of identification of amicrocalcification; iii) visual clarity of identification of anobstruction; iv) a direct comparison clarity of the first generated 2-Dprojection image; v) direct comparison identification of amicrocalcification; and vi) direct comparison clarity of identificationof an obstruction.
 18. The method of claim 15, where one or both thefirst 3-D volumetric image and the second 3-D volumetric image areDigital Breast Tomosynthesis images.
 19. The method of claim 15, wherethe first tissue is a right breast and the second tissue is a leftbreast.
 20. A system comprising: one or more client digital dataprocessors; a server digital data processor in communications couplingwith the one or more client digital data processors, the server digitaldata processor comprising one or more graphics processing units and anassociated memory; a program, executing on the server digital dataprocessor, the program computing a plurality of generated 2-D projectionimages of a 3-D Digital Breast Tomosynthesis volumetric image using aplurality of viewing directions and caching the plurality of generated2-D projection images in the associated memory; analyzing one or moregenerated 2-D projection images using bricking to identify changes inintensity density of a plurality of voxel matrices representing theplurality of generated 2-D projection images to select three or moregenerated 2-D projection images identifying an obstruction; anddisplaying on the one or more client digital data processors the threeor more generated 2-D projection images as a dynamic comparison.